We have a new generator, since we live in a third world country where PG&E is unable to provide reliable electricity. It works pretty well, a fancy Generac standby unit with load shedding. Even has a decent website monitoring the generator via WiFi, also there’s hacker software for reading the generator’s state from a serial diagnostic port.
Anyway, when we’re on generator power the UPS units sometimes complain, switch to battery power briefly. I think I’ve also noticed the lights flickering. That got me worried the generator was putting out bad power so I hooked up my IoTaWatt to monitor the AC power.
The IoTaWatt’s main function is to monitor power draw through individual circuits. It directly measures current. But it also monitors voltage and frequency via an AC transformer sensor. Near as I can tell it samples that data many times a second but the most detailed data I can get from the status API is once a second. The most detailed graphs are every 5 seconds.
As the above graph shows, the voltage and power doesn’t really change much when we switch over to generator power. Both PG&E and the generator are providing about 122V. The generator’s frequency isn’t quite as stable as PG&E was but a variance of ±0.1Hz isn’t that bad. (PG&E sometimes approaches that variance too.)
The graph above shows what happened as 12:17:30, one of the times my UPS kicked in. Turns out just then the well pump turned on (the red line), adding about 1.5kW load (or about double total power, the blue line) in that instant. The generator didn’t quite react fast enough. The power draw of some other loads (yellow and purple, basically room lights) dips briefly. More telling: the frequency of power, the black line, drops significantly, by nearly 0.15Hz. That’s the sign the generator is overloaded, it starts running more slowly and the frequency drops. It recovers quickly enough, but it’s enough to make a sensitive UPS unhappy and cause a visible flicker in the lights. Note the voltage (green line) doesn’t notably drop; I imagine the generator has a voltage regulator that smooths this out.
So that’s why the lights flicker and the UPS complains. I think that’s just a limitation of a consumer generator. It’s plenty of power to make everything run, but it’s not quite as clean as when you have utility power.
Looking at this reminded me to take another look at what the well pump was doing.
It’s still coming on every 30 minutes or so even when there’s no water demand at all, which suggests a leak somewhere. I know it’s not outside, because I turned that valve off. I’m pretty sure it’s not inside either, I’d have noticed. Maybe the well is leaking back into itself, against the check valve? Dunno. Like I said before it’s wasting about $0.50 of electricity a day, but otherwise seems mostly harmless.
Above is a cumulative graph of well power usage over 24 hours (blue) with transitory power (green). As you can see we use a lot of water overnight, when the irrigation is running, about 5kWH or $2 worth. The well doesn’t stay on continuously for much of this, other than one period about 6:15am. Our water system has no buffer of any kind; no tanks or reservoirs.